Method, device and program for coding and decoding acoustic parameter, and method, device and program for coding and decoding sound

ABSTRACT

In coding and decoding an acoustic parameter, a weighted vector is generated by multiplying a code vector output in a past frame and a code vector selected in a present frame by weighting factors respectively selected from a factor code book and adding the products to each other.

TECHNICAL FIELD

[0001] This invention relates to methods of coding and decoding low-bitrate acoustic signals in the mobile communication system and Internetwherein acoustic signals, such as speech signals and music signals, areencoded and transmitted, and also relates to acoustic parameter codingand decoding methods and devices applied thereto, and programs forconducting these methods by a computer.

PRIOR ART

[0002] In the fields of digital mobile communication and speech storage,in order to effectively utilize radio waves and storage media, therehave been used speech coding devices wherein the speech information iscompressed and encoded with high efficiency. In these speech codingdevices, in order to express the high-quality speech signals even at thelow bit rate, there has been employed a system using a model suitablefor expressing the speech signals. As a system which has been widely inactual use at the bit rates in the range of 4 kbit/s to 8 kbit/s, forexample, CELP (Code Excited Linear Prediction: Code Excited LinearPrediction Coding) system can be named. The art of CELP has beendisclosed in M. R. Schroeder and B. S. Atal: “Code-Excited LinearPrediction (CELP): High-quality Speech at Very Low Bit Rates”, Proc.ICASSP-85, 25.1.1, pp.937-940, 1985”.

[0003] The CELP type speech coding system is based on a speech syntheticmodel corresponding to a vocal tract mechanism of human being, and afilter expressed by a linear predictive coefficient indicating a vocaltract characteristics and an excitation signal for driving the filtersynthesize the speech signal. More particularly, a digitalized speechsignal is delimited by every certain length of a frame (about 5 ms to 50ms) to carry out the linear prediction of the speech signal for everyframe, so that a predicted residual error (excitation signal) is encodedby using an adaptive code vector formed of a known waveform and a fixedcode vector. The adaptive code vector is stored in an adaptive codebookas a vector which expresses a driving sound source signal generated inthe past, and is used for expressing periodic components of the speechsignal. The fixed code vector is stored in a fixed codebook as a vectorprepared in advance and having a predetermined number of waveforms, andthe fixed code vector is used for mainly expressing aperiodic componentswhich can not be expressed by the adaptive codebook. As the vectorstored in the fixed codebook, a vector formed of a random noise sequenceand a vector expressed by a combination of several pulses are used.

[0004] As a representative example of the fixed codebooks that expressthe fixed code vectors by the combination of several pulses, there is analgebraic fixed codebook. More specific contents of the algebraic fixedcodebook are shown in “ITU-T Recommendation G. 729” and the like.

[0005] In the conventional speech coding system, the linear predictivecoefficients of the speech are converted into parameters, such aspartial autocorrelation (PARCOR) coefficients and line spectrum pairs(LSP: Line Spectrum Pairs, also called as line spectrum frequencies),and quantized further to be converted into the digital codes, and thenthey are stored or transmitted. The details of these methods aredescribed in “Digital Speech Processing” (Tokai University Press)written by Sadaoki Furui, for example.

[0006] In the coding of the linear predictive coefficients, as a methodof coding the LSP parameter, a quantized parameter of the current frameis expressed by a weighted vector in which a code vector outputted fromthe vector codebook in a one or more frames in the past is multiplied bya weighting coefficient selected from a weighting coefficient codebook,or a vector in which a mean vector, found in advance, of the LSPparameter in the entire speech signal is added to this vector, and acode vector which should be outputted by the vector codebook and a setof weighting coefficients that should be outputted by the weightingcoefficient codebook are selected such that a distortion with respect tothe LSP parameter found from an input speech in the quantized parameter,that is, the quantization distortion becomes minimum or small enough.Then, they are outputted as codes of the LSP parameter.

[0007] This is generally called a weighted vector quantization, orsupposing that the weighting coefficients are considered as thepredictive coefficients from the past, it is called a moving average(MA: Moving Average) prediction vector quantization.

[0008] In a decoding side, from the received vector code and theweighting coefficient code, the code vector in the current frame and thepast code vector are multiplied by the weighting coefficient, or, avector, in which the mean vector, found in advance, of the LSP parameterin the entire speech signal is added further, is outputted as aquantized vector in the current frame.

[0009] As a vector codebook that outputs the code vector in each frame,there can be structured a basic one-stage vector quantizer, a splitvector quantizer wherein dimensions of the vector are divided, a multistage vector quantizer having two or more stages, or a multi-stage andsplit vector quantizer in which the multi stage vector quantizer and thesplit vector quantizer are combined.

[0010] In the aforementioned conventional LSP parameter encoder anddecoder, since the number of frames is large in a silent interval and astationary noise interval, and in addition, since the coding process anddecoding process are configured in multi stages, it was not alwayspossible to output the vector such that the parameter synthesized incorrespondence with the silent interval and the stationary noiseinterval can be changed smoothly. This is because of the followingreasons. Normally, the vector codebook used for coding was found bylearning, but since learned speeches did not contain enough amount ofthe silent interval or the stationary noise interval upon this learning,the vector corresponding to the silent interval or the stationary noiseinterval was not always reflected enough to learn, or if the number ofbits given to the quantizer was small, it was impossible to design thecodebook including sufficient quantized vectors corresponding tonon-voice intervals.

[0011] In these LSP parameter encoder and decoder, upon coding at thetime of actual communication, the quantization performance during thenon-voice interval could not be fully exhibited, and a deterioration ofthe quality as the reproduced sound was inevitable. Also, these problemsoccurred not only in the coding of the acoustic parameter equivalent tothe linear predictive coefficient expressing a spectrum envelope of thespeech signal, but also in the similar coding with respect to a musicsignal.

[0012] The present invention has been made in view of the foregoingpoints, and an object of the invention is to provide acoustic parametercoding and decoding methods and devices, wherein outputting the vectorsequivalent to the silent interval and the stationary noise interval isfacilitated so that the deterioration of the quality is scarce at theseintervals in the conventional coding and decoding of the acousticparameter equivalent to the linear predictive coefficient expressing aspectrum envelope of the acoustic signal, and also to provide acousticsignal coding and decoding methods and devices using the aforementionedmethods and devices, and a program for conducting these methods by acomputer.

DISCLOSURE OF THE INVENTION

[0013] The present invention is mainly characterized in that in codingand decoding of an acoustic parameter equivalent to a linear predictivecoefficient showing a spectrum envelope of an acoustic signal, that is,a parameter such as an LSP parameter, a parameter, PARCOR parameter orthe like (hereinafter simply referred to as an acoustic parameter), anacoustic parameter vector code a substantially flat spectrum envelopecorresponding to a silent interval or stationary noise interval, whichcan not originally obtained by learning by a codebook, and a vector areadded to a codebook, to thereby be selectable. The present invention isdifferent from the prior art in that a vector including a component ofthe acoustic parameter vector showing the substantially flat spectrumenvelope is obtained in advance by calculation and stored as one of thevectors of the vector codebook, and in a multi-stage quantizationconfiguration and a split vector quantization configuration, theaforementioned code vector is outputted.

[0014] An acoustic parameter coding method according to the presentinvention comprises:

[0015] (a) a step of calculating an acoustic parameter equivalent to alinear predictive coefficient showing a spectrum envelope characteristicof an acoustic signal for every frame of a predetermined length of time;

[0016] (b) a step of multiplying a code vector outputted in at least oneframe in the closest past selected from a vector codebook for storing aplurality of code vectors in correspondence with an index representingthe code vectors and a code vector selected in a current framerespectively with a set of weighting coefficients selected from acoefficient codebook for storing one or more sets of weightingcoefficients in correspondence with an index representing the weightingcoefficients, wherein multiplied results are added to generate aweighted vector and a vector including a component of the weightedvector is found as a candidate of a quantized acoustic parameter withrespect to the acoustic parameter of the current frame; and

[0017] (c) a step of determining the code vector of the vector codebookand the set of the weighting coefficients of the coefficient codebook byusing a criterion such that a distortion of the candidate of thequantized acoustic parameter with respect to the calculated acousticparameter becomes a minimum, wherein an index showing the determinedcode vector and the determined set of the weighting coefficients aredetermined and outputted as a quantized code of the acoustic parameter;and

[0018] the vector codebook includes a vector having a component of anacoustic parameter vector showing the aforementioned substantially flatspectrum envelope as one of the stored code vectors.

[0019] An acoustic parameter decoding method according to the presentinvention comprises:

[0020] (a) a step of outputting a code vector corresponding to an indexexpressed by a code inputted for every frame and a set of weightingcoefficients from a vector codebook, which stores a plurality of codevectors of an acoustic parameter equivalent to a linear predictivecoefficient showing a spectrum envelope characteristic of an acousticsignal in correspondence with an index representing the code vectors,and a coefficient codebook, which stores one or more sets of weightingcoefficients in correspondence with an index representing the sets; and

[0021] (b) a step of multiplying the code vector outputted from thevector codebook in at least one frame of the closest past and a codevector outputted from the vector codebook in a current framerespectively with the outputted set of the weighting coefficients, andadding multiplied results together to thereby generate a weightedvector, wherein a vector including a component of the weighted vector isoutputted as a decoded quantized vector of the current frame; and

[0022] the vector codebook includes a vector having a component of anacoustic parameter vector showing a substantially flat spectrum envelopeas one of the code vectors stored therein.

[0023] An acoustic parameter coding device according to the presentinvention comprises:

[0024] parameter calculating means for analyzing an input acousticsignal for every frame and calculating an acoustic parameter equivalentto a linear predictive coefficient showing a spectrum envelopecharacteristic of the acoustic signal;

[0025] a vector codebook for storing a plurality of code vectors incorrespondence with an index representing the vectors;

[0026] a coefficient codebook for storing one or more sets of weightingcoefficients in correspondence with an index representing thecoefficients;

[0027] quantized parameter generating means for multiplying a codevector with respect to a current frame outputted from the vectorcodebook and a code vector outputted in at least one frame of theclosest past respectively with the set of the weighting coefficientsselected from the coefficient codebook, the quantized parametergenerating means adding results together to thereby generate a weightedvector, the quantized parameter generating means outputting a vectorincluding a component of the generated weighted vector as a candidate ofa quantized acoustic parameter with respect to the acoustic parameter inthe current frame;

[0028] a distortion computing part for computing a distortion of thequantized acoustic parameter with respect to the acoustic parametercalculated at the parameter calculating means; and

[0029] it is configured that a codebook search controlling part fordetermining the code vector of the vector codebook and the set of theweighing coefficients of the coefficient codebook by using a criterionsuch that the distortion becomes small, the codebook search controllingpart outputting indexes respectively representing the determined codevector and the set of the weighting coefficients as codes of theacoustic parameter; and

[0030] the vector codebook includes a vector having a component of anacoustic parameter vector showing a substantially flat spectrumenvelope.

[0031] An acoustic parameter decoding device according to the presentinvention is configured to comprise:

[0032] a vector codebook for storing a plurality of code vectors of anacoustic parameter equivalent to a linear predictive coefficient showinga spectrum envelope characteristic of an acoustic signal incorrespondence with an index representing the code vectors,

[0033] a coefficient codebook for storing one or more sets of weightingcoefficients in correspondence with an index representing the weightingcoefficients, and

[0034] quantized parameter generating means for outputting one codevector from the vector codebook in correspondence with an index showinga code inputted for every frame, to thereby output a set of weightingcoefficients from the coefficient codebook, the quantized parametergenerating means multiplying the code vector outputted in a currentframe and a code vector outputted in at least one frame of the closestpast respectively with the set of the weighting coefficients outputtedin the current frame, the quantized parameter generating means addingmultiplied results together to thereby generate a weighted vector andoutputting a vector including a component of the generated weightedvector as a decoded quantized acoustic parameter of the current frame;and

[0035] the vector codebook stores a vector including a component of anacoustic parameter showing a substantially flat spectrum envelope as oneof the code vectors.

[0036] An acoustic signal coding device for encoding an input acousticsignal according to the present invention is configured to comprise:

[0037] means for encoding a spectrum characteristic of an input acousticsignal by using the aforementioned acoustic parameter coding method;

[0038] an adaptive codebook for holding adaptive code vectors showingperiodic components of the input acoustic signal therein;

[0039] a fixed codebook for storing a plurality of fixed vectorstherein;

[0040] filtering means for inputting as an excitation signal a soundsource vector generated based on the adaptive code vector from theadaptive codebook and the fixed vector from the fixed codebook, thefiltering means synthesizing a synthesized acoustic signal by using afilter coefficient based on the quantized acoustic parameter; and

[0041] means for determining an adaptive code vector and a fixed codevector respectively selected from the fixed codebook and the adaptivecodebook such that a distortion of the synthesized acoustic signal withrespect to the input acoustic signal becomes small, the means outputtingan adaptive code and a fixed code respectively corresponding to thedetermined adaptive code vector and the fixed vector.

[0042] An acoustic signal decoding device for decoding an input code andoutputting an acoustic signal according to the present invention isconfigured to comprise:

[0043] means for decoding an acoustic parameter equivalent to a linearpredictive coefficient showing a spectrum envelope characteristic froman inputted code by using the aforementioned acoustic parameter decodingmethod;

[0044] a fixed codebook for storing a plurality of fixed vectorstherein;

[0045] an adaptive codebook for holding adaptive code vectors showingperiodic components of a synthesized acoustic signal therein;

[0046] means for taking out a corresponding fixed vector from the fixedcodebook and taking out a corresponding adaptive code vector from theadaptive codebook by an inputted adaptive code and an inputted fixedcode, the means synthesizing the vectors and generating an excitationvector; and

[0047] filtering means for setting a filter coefficient based on theacoustic parameter and reproducing an acoustic signal by the excitationvector.

[0048] An acoustic signal coding method for encoding an input acousticsignal according to the present invention comprises:

[0049] (A) a step of encoding a spectrum characteristic of an inputacoustic signal by using the aforementioned acoustic parameter codingmethod;

[0050] (B) a step of using as an excitation signal a sound source vectorgenerated based on an adaptive code vector from an adaptive codebook forholding adaptive code vectors showing periodic components of an inputacoustic signal therein and a fixed vector from a fixed codebook forstoring a plurality of fixed vectors therein, and carrying out asynthesis filter process by a filter coefficient based on the quantizedacoustic parameter to thereby generate a synthesized acoustic signal;and

[0051] (C) a step of determining an adaptive code vector and a fixedvector selected from the fixed codebook and the adaptive codebook suchthat a distortion of the synthesized acoustic signal with respect to theinput acoustic signal becomes small, and outputting an adaptive code anda fixed code respectively corresponding to the determined adaptive codevector and the fixed vector.

[0052] An acoustic signal decoding method for decoding input codes andoutputting an acoustic signal according to the present inventioncomprises:

[0053] (A) a step of decoding an acoustic parameter equivalent to alinear predictive coefficient showing a spectrum envelope characteristicfrom inputted codes by using the aforementioned acoustic parameterdecoding method;

[0054] (B) a step of taking out an adaptive code vector from an adaptivecodebook for holding therein adaptive code vectors showing periodiccomponents of an input acoustic signal by an inputted adaptive code andan inputted fixed code, taking out a corresponding fixed vector from afixed codebook for storing a plurality of fixed vectors therein, andsynthesizing the adaptive code vector and the fixed vector to therebygenerate an excitation vector; and

[0055] (C) a step of carrying out a synthesis filter process of theexcitation vector by using a filter coefficient based on the acousticparameter, and reproducing a synthesized acoustic signal.

[0056] The aforementioned invention can be provided in a form of aprogram which can be conducted in the computer.

[0057] According to the present invention, in the weighted vectorquantizer (or, MA prediction vector quantizer), since a vector includinga component of an acoustic parameter vector showing a substantially flatspectrum is found and stored as the code vector of the vector codebook,a quantized vector equivalent to the corresponding silent interval orthe stationary noise interval can be outputted.

[0058] Also, according to another embodiment of the invention, as aconfiguration of a vector codebook comprised in the acoustic parametercoding device and decoding device, in the case of using a multi-stagevector codebook, a vector including a component of an acoustic parametervector showing a substantially spectrum envelope is stored a codebook ofone stage thereof, and a zero vector is stored in the codebooks of theother stages. Accordingly, an acoustic parameter equivalent to acorresponding silent interval or stationary noise interval can beoutputted.

[0059] It is not always necessary to store the zero vector. In the caseof not storing the zero vector, when the vector including the componentof the acoustic parameter vector showing the substantially flat spectrumenvelope from a codebook of one stage is selected, it will suffice thatthe vector including the component of the acoustic parameter vectorshowing the substantially flat spectrum envelope is outputted as acandidate of the code vector of the current frame.

[0060] Also, in the case that the vector codebook is formed of a splitvector codebook, there are used a plurality of split vectors in whichdimensions of vectors including a component of an acoustic parametervector showing a substantially flat spectrum envelope are divided, andby divisionally storing these split vectors one by one in a plurality ofsplit vector codebooks, respectively, when searching in the respectivesplit vector codebooks, the respective split vectors are selected, and avector by integrating these split vectors can be outputted as aquantized vector equivalent to the corresponding silent interval or thestationary noise interval.

[0061] Furthermore, the vector quantizer may be formed to have themulti-stage and split quantization configuration, and by combining thearts of the aforementioned multi-stage vector quantization configurationand the split vector quantization configuration, there can be outputtedas the quantized vector equivalent to the acoustic parameter incorrespondence with the corresponding silent interval or the stationarynoise interval.

[0062] In the case that the codebook is structured as the multi-stageconfiguration, in correspondence with respective code vectors of thecodebook at the first stage, scaling coefficients respectivelycorresponding to the codebooks on and after the second stage areprovided as the scaling coefficient codebook. The scaling coefficientscorresponding to the code vector selected at the codebook of the firststage are read out from the respective scaling coefficient codebooks,and multiplied with code vectors respectively selected from the codebookof the second stage, so that the coding with much smaller distortion ofthe quantization can be achieved.

[0063] As described above, the acoustic parameter coding and decodingmethods and the devices in which the quality deterioration is scarce inthe aforementioned interval, that is, the object of the invention, canbe provided.

[0064] In the acoustic signal coding device of the invention, in thequantization of the linear predictive coefficient, any one of theaforementioned parameter coding devices is used in an acoustic parameterarea equivalent to the linear predictive coefficient. According to thisconfiguration, the same operation and effects as those of theaforementioned one can be obtained.

[0065] In the acoustic signal decoding device of the invention, indecoding of the linear predictive coefficient, any one of theaforementioned parameter coding devices is used in the acousticparameter area equivalent to the linear predictive coefficient.According to this configuration, the same operation and effects as thoseof the aforementioned one can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

[0066]FIG. 1 is a block diagram showing a functional configuration of anacoustic parameter coding device to which a codebook according to thepresent invention is applied.

[0067]FIG. 2 is a block diagram showing a functional configuration of anacoustic parameter decoding device to which a codebook according to thepresent invention is applied.

[0068]FIG. 3 is a diagram showing an example of a configuration of avector codebook according to the present invention for LSP parametercoding and decoding.

[0069]FIG. 4 is a diagram showing an example of a configuration of avector codebook according to the present invention in case of a multistage structure.

[0070]FIG. 5 is a diagram showing an example of a configuration of avector codebook according to the present invention in the case of beingformed of a split vector codebook.

[0071]FIG. 6 is a diagram showing an example of a configuration ofvector codebook according to the present invention in the case that ascaling coefficient is adopted in the multi stage vector codebook.

[0072]FIG. 7 is a diagram showing an example of a configuration of avector codebook according to the present invention in the case that asecond stage codebook is formed of the split vector codebook.

[0073]FIG. 8 is a diagram showing an example of a configuration of avector codebook in the case that scaling coefficients are respectivelyadopted in two split vector codebooks in the codebook of FIG. 7.

[0074]FIG. 9 is a diagram showing an example of a configuration of avector codebook in the case that each stage in the multi stage codebookof FIG. 4 is structured as the split vector codebook.

[0075]FIG. 10A is a block diagram showing an example of a configurationof a speech signal transmission device to which the coding methodaccording to the present invention is applied.

[0076]FIG. 10B is a block diagram showing an example of a configurationof a speech signal receiving device to which the decoding methodaccording to the present invention is applied.

[0077]FIG. 11 is a diagram showing a functional configuration of aspeech signal coding device to which the coding method according to thepresent invention is applied.

[0078]FIG. 12 is a diagram showing a functional configuration of aspeech signal decoding device to which the decoding method according tothe present invention is applied.

[0079]FIG. 13 is a diagram showing an example of a configuration in thecase that the coding device and the decoding device according to thepresent invention are put into operation by a computer.

[0080]FIG. 14 is a graph for explaining effects of the presentinvention.

THE BEST MODE FOR CARRYING OUT THE INVENTION

[0081] First Embodiment

[0082] Next, embodiments of the invention will be explained withreference to the drawings.

[0083]FIG. 1 is a block diagram showing an example of a configuration ofan embodiment of an acoustic parameter coding device to which a linearpredictive parameter coding method according to the present invention.The coding device is formed of a linear prediction analysis part 12; anLSP parameter calculating part 13; and a codebook 14, a quantizedparameter generating part 15, a distortion computing part 16, and acodebook search control part 17, which form a parameter coding part 10.In the figure, a series of digitalized speech signal samples, forexample, are inputted from an input terminal T1. In the linearprediction analysis part 12, the speech signal sample of every one framestored in an internal buffer is subjected to the linear predictionanalysis, to calculate a pair of linear predictive coefficients. Now,supposing the order of the linear prediction analysis is p-dimension,the p-dimensional, equivalent LSP (line spectrum pairs) parameter iscalculated from the p-dimensional linear predictive coefficient in theLSP parameter calculating part 13. The details of the processing methodthereof were described in the literature written by Furui mentionedabove. The p LSP parameters are expressed as vectors as follows.

f(n)=(f ₁(n), f ₂(n), . . . , f _(p)(n))  (1)

[0084] Here, the integer n indicates a certain frame number n, andhereinafter, the frame of this number is referred to as a frame n.

[0085] The codebook 14 is provided with a vector codebook 14A, whichstores n code vectors representing LSP parameter vectors found bylearning, and a coefficient codebook 14B which stores a set of Kweighting coefficients, and by an index Ix(n) for specifying the codevector and an index Iw(n) for specifying the weighting coefficient code,a corresponding code vector x(n) and a set of weighting coefficients(w₀, w₁, . . . , w_(m)) are outputted. The quantized parametergenerating part 15 is formed of m pieces of buffer parts 15B₁, . . . ,15B_(m), which are connected in series; m+1 pieces of multipliers 15A₀,15A₁, . . . , 15A_(m), a register 15C, and a vector adder 15D. The codevector x(n) in the current frame n which is selected as one of thecandidates from the vector codebook 14A and code vectors x(n−1), . . . ,x(n−m) which are determined with respect to the past frame n−1, . . . ,n−m are respectively multiplied by a set of the selected weightingcoefficients w₀, . . . , w_(m) at the multipliers 15A₀, 15A_(m), and theresults of multiplications are added together at the adder 15D. Further,a mean vector y_(ave), found in advance, of the LSP parameter in theentire speech signal is added to the adder 15D from the register 15C. Asdescribed above, from the adder 15D, a candidate of the quantizedvector, that is, a candidate y(n) of the LSP parameter, is generated. Asthe mean vector y_(ave), a mean vector at a voice part may be used, or azero vector may be used as described later.

[0086] When the code vector x(n) selected from the vector codebook 14Awith respect to the current frame n is substituted as

x(n)=(x ₁(n), x ₂(n), . . . , x _(p)(n))  (2)

[0087] and then, similarly, the code vector determined one frame beforeis substituted as x(n−1); the code vector determined two frame before issubstituted as x(n−2); and the code vector determined m frame before issubstituted as x(n−m); a quantized vector candidate of the currentframe, that is,

y(n)=(y ₁(n), y ₂(n), . . . , y _(p)(n))  (3)

[0088] is expressed as follows:

y(n)=w ₀ ·x(n)+Σ_(j=1) ^(m) w _(j) ·x(n−j)+y _(ave)  (4)

[0089] Here, the larger a value of m is, the better the quantizationefficiency is. However, the effect at the occurrence of a code errorextends to portions after the m frame, and in addition, in case thecoded and stored speech is reproduced from the middle thereof, it isnecessary to go back to the m frame past. Therefore, m is adequatelyselected as occasion demands. For speech communication, in case of theone frame 20 ms, the value of m is sufficient if it is 6 or more, andeven the value 1 to 3 may suffice. The number m is also called as theorder of the moving average prediction.

[0090] The candidate y(n) of the quantization obtained as describedabove is sent to the distortion computing part 16, and the quantizationdistortion with respect to the LSP parameter f(n) calculated at the LPSparameter calculating part 13 is computed. The distortion d is definedby the weighted Euclidean distance as follows.

d=Σ _(i=1) ^(p) r _(i)(f _(i)(n)−y _(i)(n))²  (5)

[0091] Incidentally, r_(i), i=1, . . . , p are weighting coefficientsfound by the LSP parameter f(n), and if they are set to the weighting soas to stress on and around the formant frequency of the spectrum, theperformance becomes excellent.

[0092] In the codebook search part 17, pairs of the indexes Ix(n) andIw(n) given to the codebook 14 are sequentially changed, and thecalculation of the distortion d by the equation (5) as described aboveare repeated with regard to the respective pairs of the indexes, so thatfrom the code vector of the vector codebook 14A and the set of theweighting coefficients of the vector codebook 14A in the codebook 14,the one pair thereof making the distortion d as the output from thedistortion computing part 16 to be the smallest or small enough issearched, and these indexes Ix(n) and Iw(n) are sent out as the codes ofthe input LSP parameter from a terminal T2. The codes Ix(n) and Iw(n)sent out from the terminal T2 are sent to a decoder via a transmissionchannel, or stored in a memory.

[0093] When the output code vector x(n) of the current frame isdetermined, the code vectors x(n−j), j=1, . . . , m−1 in the buffer part15B_(j) of the past frame (n−j) are sequentially sent to the next bufferpart 15B_(j+1), and the code vector x(n) of the current frame n isinputted into the buffer 15B₁.

[0094] The invention is characterized in that as one of the code vectorsstored the vector codebook 14A used in the coding by the weighted vectorquantization of the LSP parameter described above or the moving averagevector quantization, in case the mean vector y_(ave) is zero, the LSPparameter vector F corresponding to the silent interval or stationarynoise interval is stored, or in case y_(ave) is not zero, a vector C₀found by subtracting y_(ave) from the LSP parameter vector F is stored.

[0095] Namely, in case y_(ave) is not zero, the LSP parameter vectorcorresponding to the silent interval or the stationary noise intervalconstitutes:

F=(F₁, F₂, . . . , F_(p))

[0096] and the code vector C₀ which should be stored in the vectorcodebook 14A in FIG. 1 is calculated as follows:

C ₀ =F−y _(ave)

[0097] In the coding by the moving average prediction at the silentinterval or the stationary noise interval, when the C₀ is selectedconsecutively throughout m frames, the quantized vector y(n) is found asfollows:${y(n)} = {{{w_{0} \cdot {x(n)}} + {\sum\limits_{j = 1}^{m}\quad {w_{j} \cdot {x\left( {n - j} \right)}}} + y_{ave}}\quad = {{{w_{0} \cdot C_{0}} + {\sum\limits_{j = 1}^{m}\quad {w_{j} \cdot C_{0}}} + y_{ave}}\quad = {{\left( {w_{0}{\sum\limits_{j = 1}^{m}\quad w_{j}}} \right) \cdot C_{0}} + y_{ave}}}}$

[0098] Here, supposing that the sum of the weighting coefficients fromw₀ to w_(m) is 1 or the value close thereto, y(n) can be outputted asthe quantized vector F found from the LSP parameter at the silentinterval or the vector close thereto, so that the coding performance atthe silent interval or the stationary noise interval can be improved. Bythe configuration as described above, the vector including the componentof the vector F is stored as one of the code vectors in the vectorcodebook 14A. As the code vector including the component of the vectorF, in case the quantized parameter generating part 15 generates thequantized vector y(n) including the component of the mean vectory_(ave), the one found by subtracting the mean vector y_(ave) from thevector F is used, and in case quantized parameter generating part 15generates the quantized vector y(n) that does not include the componentof the mean vector y_(ave), the vector F itself is used.

[0099]FIG. 2 is an example of a configuration of a decoding device towhich an embodiment of the invention is applied, and the decoding deviceis formed of a codebook 24 and a quantized parameter generating part 25.These codebook 24 and the quantized parameter generating part 25 arestructured respectively similarly to the codebook 14 and the quantizedparameter generating part 15 in FIG. 1. The indexes Ix(n) and Iw(n) asthe parameter codes sent from the coding device of FIG. 1 are inputted,and the code vector x(n) corresponding to the index Ix(n) is outputtedfrom the vector codebook 24A, and the set of weighting coefficients w₀,w₁, . . . , w_(m) corresponding to the index Iw(n) are outputted fromthe coefficient codebook 24B. The code vector x(n) respectivelyoutputted per frame from the vector codebook 24A is sequentiallyinputted into buffer parts 25B₁, . . . , 25B_(m), which are connected inseries. The code vector x(n) of the current frame n and code vectorsx(n−1), . . . , x(n−m) at 1, . . . , m frame past of the buffer parts25B₁, . . . , 25B_(m) are multiplied by weighting coefficients w₀, w₁, .. . , w_(m), in multipliers 25A₀, 25A₁, . . . , 25A_(m), and thesemultiplied results are added together at adder 25D. Further, a meanvector y_(ave) of the LSP parameter in the entire speech signal, whichis held in advance in a register 25C, is added to the adder 25D, and theaccordingly obtained quantized vector y(n) is outputted as a decodingLSP parameter. The vector y_(ave) can be the mean vector of the voicepart, or can be a zero vector z.

[0100] In the present invention, also in the decoding device, as in thecoding device shown in FIG. 1, by storing the vector C₀ as one of thecode vectors in the vector codebook 24A, the LSP parameter vector Ffound at the silent interval or the stationary noise interval of theacoustic signal can be outputted.

[0101] In case the mean vector y_(ave) is not added at the adder 15D inFIG. 1 and at the adder 25D in FIG. 2, the LSP parameter vector Fcorresponding to the silent interval and the stationary noise intervalis stored instead of the vector C₀ in the vector codebooks 14A and 24A.In the following explanations, the LSP parameter vector F or vector C₀stored in the respective vector codebooks 14A and 24A are represented byand referred to as the vector C₀.

[0102] In FIG. 3, an example of a configuration of the vector codebook14A in FIG. 1, or the vector codebook 24A is shown as a vector codebook4A. This example is the one in case one-stage vector codebook 41 isused. N pieces of code vectors x₁, . . . , x_(N) are stored as they arein the vector codebook 41, and corresponding to the inputted indexIx(n), any one of the N code vectors is selected and outputted. In thepresent invention, as one of the code vector x, the code vector C₀ isused. Although N code vectors in the vector codebook 41 is formed bylearning as in the conventional one, for example, in the presentinvention, one vector, that is most similar (distortion is small) to thevector C₀ among these vectors, is substituted by C₀, or C₀ is simplyadded.

[0103] There are several methods for finding the vector C₀. As one ofthem, since the spectrum envelope of the input acoustic signal normallybecomes flat at the silent interval or the stationary noise interval, inthe case of p-dimensional LSP parameter vector F, for example, 0 to πare divided equally by p+1, and p values having the substantially equalinterval in size, such as π/(1+p), 2π/(1+p), . . . , π/(1+p), may beused as the LSP parameter vector. Alternatively, from the actual LSPparameter vector F at the silent interval and the stationary noiseinterval, it can be found by C₀=F−y_(ave). Or, the LSP parameter in thecase of inputting the white noise or Hoth noise may be used as theparameter vector F, to find C₀=F−y_(ave). Incidentally, in general, themean vector y_(ave) of the LSP parameter among the entire speech signalis found as a mean vector of all of the vectors for learning when thecode vector x of the vector codebook 41 is learned.

[0104] The following Table 1 show examples of the ten-dimensionalvectors C₀ , y _(ave), and F wherein the LSP parameters at the silentinterval or the stationary noise interval are normalized between 0 to πwhen p=10 dimensional LSP parameters are used as the acousticparameters. TABLE 1 p C₀ y_(ave) F 1 0.0498613038 0.250504841 0.300366 20.196914087 0.376541460 0.573456 3 0.274116971 0.605215652 0.879333 40.222466032 0.923759106 1.146225 5 0.192227464 1.24066692 1.432894 60.170497624 1.54336668 1.713864 7 0.139565958 1.85979861 1.999365 80.177638442 2.10739425 2.285031 9 0.165183997 2.40568568 2.570870 100.250504841 2.68495222 2.856472

[0105] The vector F is the example of the code vector of the LSPparameter representing the silent interval and the stationary noiseinterval written into the codebook according to the present invention.Values of the elements of this vector are increased at substantiallyconstant interval, and this means that the frequency spectrum issubstantially flat.

[0106] Second Embodiment

[0107]FIG. 4 shows another example of the configuration of the vectorcodebook 14A of the LSP parameter encoder of FIG. 1 or the vectorcodebook 24A of the LSP parameter decoding device of FIG. 2, shown as acodebook 4A in case two-stage vector codebook is used. A first-stagecodebook 41 stores N pieces of p-dimensional code vectors x₁₁, . . . ,x_(1N), and a second-stage codebook 42 stores N′ pieces of p-dimensionalcode vectors x₂₁, . . . , x_(2N′).

[0108] Firstly, when the index Ix(n) specifying the code vector isinputted, the index Ix(n) is analyzed at a code analysis part 43, tothereby obtain an index Ix(n)₁ specifying the code vector at the firststage and an index Ix(n)₂ specifying the code vector at the secondstage. Then, i-th and i′-th code vectors x_(1i) and x_(2i′) respectivelycorresponding to the indexes Ix(n)₁ and Ix(n)₂ of the respective stagesare read out from the first-stage codebook 41 and the second-stagecodebook 42, and the code vectors are added together at an adding part44, to thereby output the added result as a code vector x(n).

[0109] In the case of the two-stage structure vector codebook, the codevector search is carried out by using only the first-stage codebook 41for a predetermined number of candidate code vectors sequentiallystarting from the one having the smallest quantization distortion. Thissearch is conducted by a combination with the set of the weightingcoefficients of the coefficients codebook 14B shown in FIG. 1. Then,regarding the combinations of the first-stage code vectors as therespective candidates and the respective code vectors of thesecond-stage codebook, there is searched a combination of the codevectors in which the quantization distortion is the smallest.

[0110] In case the code vector is searched by prioritizing thefirst-stage codebook 41 as described above, the code vector C₀ (or F) isprestored as one of the code vectors in the first-stage codebook 41 ofthe multi stage vector codebook 4A, as well as the zero vector z isprestored as one of the code vectors in the second stage codebook 42.Accordingly, in case the code vector C₀ is selected from the codebook41, the zero vector z is selected from the codebook 42. As a result, thepresent invention achieves the structure in which the code vector C₀ inthe case of corresponding to the silent interval or the stationary noiseinterval can be outputted as the output of the codebook 4A from theadder 44. It may be structured such that in case the zero vector z isnot stored and the code vector C₀ is selected from the codebook 41, theselection and addition from the codebook 42 are not conducted.

[0111] In case the search is conducted for all of the combinations ofthe respective code vectors in the first-stage codebook 41 and therespective code vectors in the second-stage codebook, the code vector C₀and the zero vector z may be stored in either of the codebooks as longas they are stored in the separate codebooks from each other. It ishighly possible that the code vector C₀ and the zero vector z areselected at the same time in the silent interval or the stationary noiseinterval, but they may not be always selected simultaneously in relationto the computing error and the like. In the codebooks of the respectivestages, the code vector C₀ or the zero vector z becomes a choice forselection as same as the other code vectors.

[0112] The zero vector may not be stored in the second-stage codebook42. In this case, if the vector C₀ is selected from the first-stagecodebook 41, the selection of the code vector from the second-stagecodebook 42 is not conducted, and it will suffice that the code C₀ ofthe codebook 41 is outputted as it is from the adder 44.

[0113] By forming the codebook 4A by the multi stage codebook as shownin FIG. 4, this structure is effectively the same as one in which thecode vectors are provided only in the number of combinations of theselectable code vectors, and therefore, as compared with the case formedof single stage codebook only as shown in FIG. 3, there is an advantagethat the size (the total number of the code vectors here) of thecodebook can be reduced. Although FIG. 4 shows the case of theconfiguration formed of the two-stage vector codebooks 41 and 42, incase the number of the stages is 3 or more, it will suffice thatcodebooks only in the number corresponding to the additional stages maybe added, and the code vectors are selected from the respectivecodebooks by indexes corresponding to the respective stages, to therebycarry out the vector synthesis of these vectors. Thus, it can be easilyexpanded.

[0114] Third Embodiment

[0115]FIG. 5 shows the case that in the vector codebook of theembodiment of FIG. 4, with respect to each code vector of thefirst-stage codebook 41, a predetermined scaling coefficient ismultiplied by the code vector selected from the second-stage codebook42, and the multiplied result is added to the code vector from thefirst-stage codebook 41 to be outputted. A scaling coefficient codebook45 is provided to store scaling coefficients S₁, . . . , S_(N), forexample, in the range of about 0.5 to 2, determined by learning inadvance in correspondence to the respective vectors x₁₁, . . . , C₀, . .. , x_(1N), and accessed by an index Ix(n)₁ common with the first-stagecodebook 41.

[0116] Firstly, when the index Ix(n) specifying the code index isinputted, the index Ix(n) is analyzed at the code analysis part 43, sothat the index Ix(n)₁ specifying the code vector of the first stage andthe Ix(n)₂ specifying the code vector of the second stage are obtained.The code vector x_(1i) corresponding to Ix(n)₁ is read out from thefirst-stage codebook 41. Also, from the scaling coefficient codebook 45,the scaling coefficient s_(i) corresponding to the read index Ix(n)₁.Next, the code vector x_(2i′) corresponding to the Ix(n)₂ is read outfrom the second-stage codebook 42, and in a multiplier 46, the scalingcoefficient s_(i) is multiplied by the code vector x_(2i′) from thesecond-stage codebook 42. The vector obtained by the multiplication andthe code vector x_(1i) from the first-stage codebook 41 are addedtogether at the adding part 44, and the added result is outputted as thecode vector x(n) from the codebook 4A.

[0117] Also, in this embodiment, upon searching the code vector, firstlyonly the first-stage codebook 41 is used to search a predeterminednumber of the candidate code vectors sequentially starting from the onehaving the smallest quantization distortion. Then, regardingcombinations of the respective candidate code vectors and the respectivecode vectors of the second codebook 42, a combination thereof having thesmallest quantization distortion is searched. In this case, with respectto the multi stage vector codebook 4A with the scaling coefficients, thevector C₀ is prestored as one cod vector in the first-stage codebook 41,and the zero vector z is prestored as one of the code vectors in thesecond-stage codebook 42 as well. Similarly to the case in FIG. 4, ifthe search is conducted for all of the combinations between the codevectors of two codebooks 41 and 42, the code vector C₀ and the zerovector z may be stored either of the codebooks as long as they arestored in the separate codebooks from each other. Alternatively, as inthe embodiments described previously, the zero vector z may not bestore. In that case, if the code vector C₀ is selected, the selectionand addition from the codebook 42 are not conducted.

[0118] As described above, the code vector in case of corresponding tothe silent interval or the stationary noise interval can be outputted.Although it is highly possible that the code vector C₀ and the zerovector z are selected at the same time in the silent interval or thestationary noise interval, they may not be always selectedsimultaneously in relation to the computing error and the like. In thecodebooks of the respective stages, the code vector C₀ or the zerovector z becomes a choice for selection as same as the other codevectors. As in the embodiment of FIG. 5, by using the scalingcoefficient codebook 45, this structure is effectively the same as onein which the second-stage codebook is provided only in the number N ofthe scaling coefficients, and therefore, there is an advantage that thecoding with much smaller quantization distortion can be achieved.

[0119] Fourth Embodiment

[0120]FIG. 6 is a case wherein the vector codebook 14A of the parametercoding device of FIG. 1 or the vector codebook 24A of the parameterdecoding device of FIG. 2 are formed as a split vector codebook 4A, towhich the present invention is applied. Although the codebook of FIG. 6is formed of half-split vector codebook, in case the number of divisionsis three or more, it is possible to expand similarly, so that achievingthe case wherein the number of divisions is 2 will be described here

[0121] The codebook 4A includes a low-order vector codebook 41 _(L)storing N pieces of low-order code vectors x_(L1), . . . , x_(LN), and ahigh-order vector codebook 41 _(H) storing N′ pieces of high-order codevectors x_(H1), . . . , x_(HN′). Supposing the output code vector isx(n), in the low-order and high-order codebooks 41 _(L) and 41 _(H), 1to k-orders are defined as the low order and k+1- to p-orders aredefined as the high order among p-order, so that the codebooks arerespectively formed of the vectors in the respective numbers of thedimensions. Namely, i-th vector of the low-order codebook 41 _(L) isexpressed by:

x_(Li)=(x_(Li1), x_(Li2), . . . , x_(Lik))  (9)

[0122] and i′-th vector of the high-order vector codebook 41 _(H) isexpressed by:

x_(Hi′)=(x_(Hi′k+1), x_(Hi′k+2), . . . , x_(Hi′p))  (10)

[0123] The inputted index Ix(n) is divided into Ix(n)_(L) and Ix(n)_(H),and corresponding to these Ix(n)_(L) and Ix(n)_(H), the low-order andhigh-order split vectors x_(Li) and x_(Hi′) are respectively selectedfrom the respective codebooks 41 _(L) and 41 _(H), and these splitvectors x_(Li) and x_(Hi′) are integrated at an integrating part 47, tothereby generate the output code vector x(n). In other words, supposingthat the code vector outputted from the integrating part 47 is x(n),

x(n)=(x _(Li1) , x _(Li2) , . . . , x _(Lik) |x _(Hi′k+1) , x _(Hi′k+2), . . . , x _(Hi′p))

[0124] is expressed.

[0125] In this embodiment, a low-order vector C_(0L) of the vector C₀ isstored as one of the vectors of the low-order codebook 41 _(L), and ahigh-order vector C_(0H) of the vector C₀ is stored as one of thevectors of the high-order codebook 41 _(H). As described above, there isachieved a structure which can output the following as the code vectorin case of corresponding to the silent interval or the stationary noiseinterval:

C₀=(C_(0L)|C_(0H))

[0126] Furthermore, depending on the case, the vector may be outputtedas a combination of C_(0L) and the other high-order vector, or acombination of the other low-order vector and C_(0H). If the splitvector codebooks 41 _(L) and 41 _(H) are provided as shown in FIG. 6,this is equivalent to providing the code vectors in the number ofcombinations between the two split vectors, there is an advantage that asize of each split vector codebook can be reduced.

[0127] Fifth Embodiment

[0128]FIG. 7 shows a still another example of the configuration of thevector codebook 14A of the acoustic parameter coding device of FIG. 1 orthe vector codebook 24A of the acoustic parameter decoding device ofFIG. 2, wherein the codebook 4A is formed as a multi-stage and splitvector codebook 4A. The codebook 4A is structured such that in thecodebook 4A of FIG. 4, the second-stage codebook 42 is formed of ahalf-split vector codebook as same as one in FIG. 6.

[0129] The first-stage codebook 41 N pieces of code vectors x₁₁, . . . ,x_(1N), a second-stage low-order codebook 42 _(L) stores N′ pieces oflow-order code vectors x_(2L1), . . . , x_(2LN′), and a second-stagehigh-order codebook 42 _(H) stores N″ pieces of high-order code vectorsx_(2H1), . . . , x_(2HN″).

[0130] In a code analysis part 43 ₁, the inputted index Ix(n) isanalyzed into an index Ix(n)₁ specifying the first-stage code vector,and an index Ix(n)₂ specifying the second-stage code vector. Then, i-thcode vector x_(1i) corresponding to the first-stage index Ix(n)_(i) isread out from the first-stage codebook 41. Also, the second-stage indexIx(n)₂ is analyzed into Ix(n)_(2L) and Ix(n)_(2H), and by Ix(n)_(2L) andIx(n)_(2H), the respective i′-th and i″-th split vectors x_(2Li′) andx_(2Hi″) of the second-stage low-order split vector codebook 42 _(L) andthe second-stage high-order split vector codebook 42 _(H) are selected,and these selected split vectors are integrated at the integrating part47, to thereby generate the second-stage code vector x_(2i′i″). At theadding part 44, the first-stage code vector x_(1i) and the second-stageintegrated vector x_(2i′i″) are added together, to be outputted as thecode vector x(n).

[0131] In this embodiment, as in the embodiments of FIG. 4 and FIG. 5,the vector C₀ is stored as one of the vectors of the first-stagecodebook 41, and split zero vectors Z_(L) and Z_(H) are storedrespectively as one of the vectors of the low-order split vectorcodebook 42 _(L) of the second-stage split codebook 42 and one of thevectors of the high-order split vector codebook 42 _(H) of thesecond-stage split codebook 42. As structured as above, there isachieved a structure of outputting the code vector in case ofcorresponding to the silent interval or the stationary noise interval.The number of the stages of the codebooks may be three or more. Also,the split vector codebook can be used for any of the stages, and thenumber of the split codebooks per one stage is not limited to two.Furthermore, if the search is conducted regarding the code vectors ofall of the combination between the first-stage codebook 41 and thesecond-stage codebooks 42 _(L) and 42 _(H), the vector C₀ and the splitzero vectors Z_(L) and Z_(H) may be stored any of the codebooks of thedifferent stages from each other. Alternatively, as in the second andthird embodiments, storing the split zero vectors may be omitted.

[0132] In case they are not stored, the selection and addition from thecodebooks 42 _(L) and 42 _(H) are not carried out at the time ofselecting the vector C₀.

[0133] Sixth Embodiment

[0134]FIG. 8 is a multi-stage and split vector codebook 4A with scalingcoefficients, to which the present invention is applied, wherein thelow-order codebook 42 _(L) and the high-order codebook 42 _(H) of thesplit vector codebook 42 in the vector codebook 4A of the embodiment ofFIG. 7 is provided with scaling coefficient codebooks 45 _(L) and 45_(H) similar to the scaling coefficient codebook 45 in the embodiment ofFIG. 5. As coefficients by which the low-order and the high-order splitvectors are multiplied respectively, N pieces of coefficients in thevalue of about 0.5 to 2, for example, are stored in the low-orderscaling coefficient codebook 45 _(L) and the high-order scalingcoefficient codebook 45 _(H).

[0135] At an analysis part 43 ₁, the inputted index Ix(n) is analyzedinto the index Ix(n)₁ specifying the first-stage code vector and theindex Ix(n)₂ specifying the second-stage code vector. Firstly, the codevector x_(1i) corresponding to index Ix(n)₁ is obtained from thefirst-stage codebook 41. Also, in correspondence with the index Ix(n)₁,a low-order scaling coefficient S_(Li) and a high-order scalingcoefficient S_(Hi) are respectively read out from the low-order scalingcoefficient codebook 45 _(L) and the high-order scaling coefficientcodebook 45 _(H). Then, the index Ix(n)₂ is analyzed into an indexIx(n)_(2L) and an index Ix(n)_(2H) at an analysis part 43 ₂, andrespective split vectors x_(2Li′) and x_(2Hi″) of the second-stagelow-order split vector codebook 42 _(L) and the second-stage high-ordersplit vector codebook 42 _(H) are selected by these indexes Ix(n)_(2L)and Ix(n)_(2H). These selected split vectors are multiplied by thelow-order and high-order scaling coefficients S_(Li) and S_(Hi) atmultipliers 46 _(L) and 46 _(H), and the obtained multiplied vectors areintegrated at an integrating part 47, to thereby generate a second-stagecode vector x_(2i′i″). The first-stage code vector x_(1i) and thesecond-stage integrated vector x_(2i′i″), are added together at theadder 44, and the added result is outputted as the code vector x(n).

[0136] In the multi-stage and split vector codebook 4A with scalingcoefficients of the embodiment, the vector C₀ is stored as one of thecode vectors in the first-stage codebook 41, and the split zero vectorsZ_(L) and Z_(H) are respectively stored as the split vectors in thelow-order split vector codebook 42 _(L) and the high-order split vectorcodebook 42 _(H) of the second-stage split vector codebook as well.Accordingly, there is achieved a configuration of outputting the codevector in the case of corresponding to the silent interval or thestationary noise interval. The number of the stages of the codebook maybe three or more. In this case, two or more stages subsequent to thesecond-stage can be respectively formed of the split vector codebooks.Also, in either case, it is not limited to the number of the splitvector codebooks per stage.

[0137] Seventh Embodiment

[0138]FIG. 9 illustrates a still further example of a configuration ofthe vector codebook 4A of the acoustic parameter coding device of FIG. 1of the vector codebook 24A of the acoustic parameter decoding device ofFIG. 2, and the first-stage codebook 41 of the embodiment of FIG. 7 isalso formed of split vector codebooks as in the embodiment of FIG. 6. Inthis embodiment, N pieces of high-order split vectors x_(1L1), . . . ,x_(1LN) are stored in the first-stage low-order codebook 41 _(L), and N′pieces of high-order split vectors x_(1H1), . . . , x_(HN′) are storedin the first-stage high-order codebook ⁴¹H. N″ pieces of low-order splitvectors x_(2L1), . . . , x_(2LN″) are stored in the second-stagelow-order codebook 42 _(L), and N′″ pieces of high-order split vectorsx_(2H1), . . . , x_(2HN′″) are stored in the second-stage high-ordercodebook 42 _(H).

[0139] At the code analysis part 43, the inputted index Ix(n) isanalyzed into the index Ix(n)₁ specifying the first-stage code vectorand the index Ix(n)₂ specifying the second-stage code vector. Respectivei-th and i′th split vectors x_(1Li) and x_(1Hi′) of the first-stagesplit vector codebook 41 _(L) and the first-stage high-order codebook 41_(H) are selected as vectors corresponding to the first-stage indexIx(n)₁, and the selected vectors are integrated at an integrating part47 ₁, to thereby generate a first-stage integrated vector x_(1ii′).

[0140] Also, similarly to the first stage, regarding the second-stageindex Ix(n)₂, respective i″-th and i′″th split vectors x_(2Li″) andx_(2Hi′″) of the second-stage split vector codebook 42 _(L) and thesecond-stage high-order codebook 42 _(H) are selected, and the selectedvectors are integrated at an integrating part 47 ₂, to thereby generatea second-stage integrated vector x_(2i″i′″). At the adding part 44, thefirst-stage integrated vector x_(1ii′) and the second-stage integratedvector x_(2i″i′″) are added together, and the added result is outputtedas the code vector x(n).

[0141] In this embodiment, similarly to the configuration of the splitvector codebook of FIG. 6, at the first stage, the low-order splitvector C_(0L) of the vector C₀ is stored as one of the vectors of thefirst stage low-order codebook 41 _(L), and the high-order split vectorC_(0H) of the vector C₀ is stored as one of the vectors of thefirst-stage high-order codebook 41 _(H). In addition, the split zerovectors Z_(L) and Z_(H) are respectively stored as the respective onesof vectors of the low-order split vector codebook 42 _(L) of thesecond-stage split vector codebook 42 and the high-order split vectorcodebook 42 _(H) of the second stage. According to this configuration,there is achieved a configuration which enable to output the code vectorin the case of corresponding to the silent interval or the stationarynoise interval. Also in this case, the number of the multi stages is notlimited to two, and the number of the split vector codebooks per stageis not limited to two.

[0142] Eighth Embodiment

[0143]FIG. 10 are block diagrams illustrating configurations of speechsignal transmission device and receiving device to which the presentinvention is applied.

[0144] A speech signal 101 is converted into an electric signal by aninput device 102, and outputted to an A/D converter 103. The A/Dconverter converts the (analog) signal outputted from the input device102 into a digital signal, and output it to a speech coding device 104.The speech coding device 104 encodes the digital speech signal outputtedfrom the A/D converter 103 by using a speech coding method, describedlater, and outputs the encoded information to an RF modulator 105. TheRF modulator 105 converts the speech encoded information outputted fromthe speech coding device 104 into a signal to be sent out by beingplaced on a propagation medium, such as a radio wave, and outputs thesignal to a transmitting antenna 106. The transmitting antenna 106transmits the output signal outputted from the RF modulator 105 as theradio wave (RF signal) 107. The foregoing is the configuration andoperations of the speech signal transmission device.

[0145] The transmitted radio wave (RF signal) 108 is received by areceiving antenna 109, and outputted to an RF demodulator 110.

[0146] Incidentally, the radio wave (RF signal) 108 in the figureconstitutes the radio wave (RF signal) 107 as seen from the receivingside, and if there is no damping of signal or superposition of the noisein the propagation channel, the radio wave 108 constitutes the exactlysame one as the radio wave (RF signal) 107. The RF demodulator 110demodulates the speech encoded information from the RF signal outputtedfrom the receiving antenna 109, and outputs the same to a speechdecoding device 111. The speech decoding device 111 decodes the speechsignal from the speech encoded information by using the speech decodingmethod, described later, and outputs the same to a D/A converter 112.The D/A converter 112 converts the digital speech signal outputted fromthe speech decoding device 111 into an analog electric signal and outputit to an output device 113. The output device 113 converts the electricsignal into vibration of air, and outputs as a sound wave 114 so thatthe human being can hear by ears. The foregoing is the configuration andoperations of the speech signal receiving device.

[0147] By having at least one of the aforementioned speech signaltransmission device and receiving device, a base station and mobileterminal device in the mobile communication system can be structured.

[0148] The aforementioned speech signal transmission device ischaracterized in the speech coding device 104. FIG. 11 is a blockdiagram illustrating a configuration of the speech coding device 104.

[0149] An input speech signal constitutes the signal outputted from theA/D converter 103 in FIG. 10, and is inputted into a preprocessing part200. In the preprocessing part 200, there are conducted a waveformshaping process and a preemphasis process, which might be connected toimprovement of performances in high-pass filter processing for removingDC components or subsequent coding process, and a processed signal Xinis outputted to an LPC analysis part 201 and an adder 204, and then to aparameter determining part 212. The LPC analysis conducts the linearprediction analysis of Xin, and the analyzed result (linear predictivecoefficient) is outputted to an LPC quantization part 202. The LPCquantization part 202 is formed of an LSP parameter calculating part 13,a parameter coding part 10, a decoding part 18, and a parameterconverting part 19. The parameter coding part 10 has the sameconfiguration as the parameter coding part 10 in FIG. 1 to which thevector codebook of the invention according to one of the embodiments ofFIGS. 3 to 9 is applied. Also, the decoding part 18 has the sameconfiguration as the decoding device in FIG. 2, to which one of thecodebooks of FIGS. 3 to 9.

[0150] The linear predictive coefficient (LPC) outputted from the LPCanalysis part 201 is converted into the LSP parameter at the LSPparameter calculating part 13, and the obtained LSP parameter is encodedat the parameter coding part 10 as explained with reference to FIG. 1.The vectors Ix(n) and Iw(n) obtained by encoding, that is, the code Lshowing the quantized LPC is outputted to a multiplexing part 213. Atthe same time, these codes Ix(n) and Iw(n) are decoded at the decodingpart 18 to obtain the quantized LSP parameter, and the quantized LSPparameter is converted again into the LPC parameter at the parameterconverting part 19, so that the obtained quantized LPC parameter isgiven to a synthesis filter 203. By having the quantized LPC as a filtercoefficient, the synthesis filter 203 synthesizes the acoustic signal bya filter process with respect to a drive sound source signal outputtedfrom an adder 210, and outputs the synthesized signal to the adder 204.

[0151] The adder 204 calculates an error signal ε between theaforementioned Xin and the aforementioned synthesized signal, andoutputs the same to a perceptual weighting part 211. The perceptualweighting part 211 conducts the perceptual weighting with respect to theerror signal ε outputted from the adder 204, and calculates a distortionof the synthesized signal with respect to Xin in a perceptual weightingarea, to thereby output it to the parameter determining part 212. Theparameter determining part 212 determines the signals that should begenerated by an adaptive codebook 205, a fixed codebook 207 and aquantized gain generating part 206 such that the coding distortionoutputted from the perceptual weighting part 211 becomes a minimum.Incidentally, not only minimizing the coding distortion outputted fromthe perceptual weighting part 211, but also using a method of minimizinganother coding distortion by using the aforementioned Xin, to therebydetermine the signal generated from the aforementioned three means, thecoding performance can be further improved.

[0152] The adaptive codebook 205 conducted buffering of the sound sourcesignal of the preceding frame n−1, that was outputted from the adder 210in the past when the distortion was minimized, and cuts out the soundvector from a position specified by an adaptive vector code A thereofoutputted from the parameter determining part 212, to thereby repeatedlyconcatenate the same until it becomes the length of one frame, resultingin generating the adaptive vector including a desired periodic componentand outputting the same to a multiplier 208. In the fixed codebook 207,a plurality of fixed vectors each having the length of one frame arestored in correspondence with the fixed vector codes, and outputs afixed vector, which has a form specified by a fixed vector code Foutputted from the parameter determining part 212, to a multiplier 209.

[0153] The quantized gain generating part 206 respectively provides themultipliers 208 and 209 with an adaptive vector, that is specified by again code G outputted from the parameter determining part 212, aquantized adaptive vector gain g_(A) and a quantized adaptive vectorgain g_(F) with respect to the fixed vector. In the multiplier 208, thequantized adaptive vector gain g_(A) outputted from the quantized gaingenerating part 206 is multiplied by the adaptive vector outputted fromthe adaptive codebook 205, and the multiplied result is outputted to theadder 210. In the multiplier 209, the quantized fixed vector gain g_(F)outputted from the quantized gain generating part 206 is multiplied bythe fixed vector outputted from the fixed codebook 207, and themultiplied result is outputted to the adder 210.

[0154] In the adder 210, the adaptive vector and the fixed vector aftermultiplying with the gains are added together, and the added result isoutputted to the synthesis filter 203 and the adaptive codebook 205.Finally, in the multiplexing part 213, the code L indicating thequantized LPC is inputted from the LPC quantization part 202; theadaptive vector code A indicating the adaptive vector, the fixed vectorcode F indicating the fixed vector, and the gain code G indicating thequantized gains are inputted from the parameter determining part 212;and these codes are multiplexed to be outputted as the encodedinformation to the transmission path.

[0155]FIG. 12 is a block diagram illustrating a configuration of thespeech decoding device 111 in FIG. 10.

[0156] In the figure, regarding the encoded information outputted fromthe RF demodulator 110, the multiplexed encoded information is separatedby a demultiplexing part 1301 into individual codes L. A, F and G. Theseparated LPC code L is given to an LPC decoding part 1302; theseparated adaptive vector code A is given to an adaptive codebook 1305;the separated gain code G is given to a quantized gain generating part1306; and the separated fixed vector code F is given to a fixed codebook1307. The LPC decoding part 1302 is formed of a decoding part 1302Aconfigured as same as that of FIG. 2, and a parameter converting part1302B. The code L=(Ix(n), Iw(n)) provided from the demultiplexing part1301 is decoded in the LSP parameter area by the decoding part 1302A asshown in FIG. 2, and converted into an LPC, to thereby be outputted to asynthesis filter 1303.

[0157] The adaptive codebook 1305 takes out an adaptive vector from aposition specified by the adaptive vector code A outputted from thedemultiplexing part 1301, and outputs the same to a multiplier 1308. Thefixed codebook 1307 generates a fixed vector specified by the fixedvector code F outputted from the demultiplexing part 1301, and outputsthe same to a multiplier 1309. The quantized gain generating part 1306decodes the adaptive vector gain g_(A) and the fixed vector gain g_(F),which are specified by the gain code G outputted from the demultiplexingpart 1301, and respectively output them to the multipliers 1308 and1309. In the multiplier 1308, the adaptive code vector is multiplied bythe aforementioned adaptive code vector gain g_(A), and the multipliedresult is outputted to an adder 1310. In the multiplier 1309, the fixedcode vector is multiplied by the aforementioned fixed code vector gaing_(F), and the multiplied result is outputted to the adder 1310. In theadder 1310, the adaptive vector and the fixed vector, which areoutputted from the multipliers 1308 and 1309 after multiplying with thegains, are added together, and the added result is outputted to thesynthesis filter 1303. In the synthesis filter 1303, by having thevector outputted from the adder 1310 as a drive sound source signal, thefilter synthesis is conducted by using a filter coefficient decoded bythe LPC decoding part 1302, and the synthesized signal is outputted to apostprocessing part 1304. The postprocessing part 1304 conducts aprocess for improving a subjective quality of the speech, such asformant emphasis or pitch emphasis, or conducts a process for improvinga subjective quality of the stationary noise, and thereafter outputs asa final decoded speech signal.

[0158] Although the LSP parameter is used as the parameter equivalent tothe linear predictive coefficient indicating the spectrum envelope inthe aforementioned description, other parameters, such as α parameter,PARCOR coefficient and the like, can be used. In the case of using theseparameters, since the spectrum envelope also becomes flat in the silentinterval or the stationary noise interval, the computation of theparameter at these intervals can be conducted easily, and in the case ofp-order α parameter, for example, it will suffice that 0-order is 1.0and 1- to p-order is 0.0. Even in the case of using other acousticparameters, a vector of the acoustic parameter determined to indicatesubstantially flat spectrum envelope will suffice. Incidentally, the LSPparameter is practical since the quantization efficiency thereof isgood.

[0159] In the foregoing description, in the case that the vectorcodebook is structured as the multi-stage configuration, the vector C₀may be expressed by two synthesis vectors, for example, C₀=C₀₁+C₀₂, andC₀₁ and C₀₂ may be stored in the codebooks of the different stages fromeach other.

[0160] Furthermore, the present invention is applied not only to codingand decoding of the speech signal, but also to coding and decoding ofgeneral acoustic signal, such as a music signal.

[0161] Also, the device of the invention can carry out coding anddecoding of the acoustic signal by running the program by the computer.FIG. 13 illustrates an embodiment in which a computer conducts theacoustic parameter coding device and decoding device of FIGS. 1 and 2using one of the codebooks of FIGS. 3 to 9, and the acoustic signalcoding device and the decoding device of FIGS. 11 and 12 to which thecoding method and decoding method thereof are applied.

[0162] The computer which carries out the present invention is formed ofa modem 410 connected to a communication network; an input and outputinterface 420 for inputting and outputting the acoustic signal; a buffermemory 430 for temporarily storing a digital acoustic signal or theacoustic signal; a random access memory (RAM) 440 for carrying out thecoding and decoding processes therein; a central processing unit (CPU)450 for controlling the input and output of the data and programexecution; a hard disk 460 in which the coding and decoding program isstored; and a drive 470 for driving a record medium 470M. Thesecomponents are connected by a common bus 480.

[0163] As the record medium 470M, there can be used any kinds of recordmedia, such as a compact disc CD, a digital video disc DVD, amagneto-optical disk MO, a memory card, and the like. In the hard disk460, there is stored the program in which the coding method and thedecoding method conducted in the acoustic signal coding device anddecoding device of FIGS. 11 and 12 are expressed by procedures by thecomputer. This program includes a program, as a subroutine, for carryingout the acoustic parameter coding and decoding of FIGS. 1 and 2.

[0164] In the case of encoding the input acoustic signal, CPU 450 loadsan acoustic signal coding program from the hard disk 460 into RAM 440;the acoustic signal imported into the buffer memory 430 is encoded byconducting the process per frame in RAM 440 in accordance with thecoding program; and obtained code is send out as the encoded acousticsignal data via the modem 410, for example, to the communicationnetwork. Alternatively, the data is temporarily saved in the hard disk460. Or, the data is written on the record medium 470M by the recordmedium drive 470.

[0165] In the case of decoding the input encoded acoustic signal, CPU450 loads a decoding program from the hard disk 460 into RAM 440. Then,the acoustic code data is downloaded to the buffer memory 430 via themodem 410 from the communication network, or loaded to the buffer memory430 from the record medium 470M by the drive 470. CPU 440 processes theacoustic code data per frame in RAM 440 in accordance with the decodingprogram, and obtained acoustic signal data is outputted from the inputand output interface 420.

[0166] Effect of the Invention

[0167] Table 1 of FIG. 14 shows quantization performances of theacoustic parameter coding devices in the case of embedding the zerovector C₀ at the silent interval and the zero vector z in the codebookaccording to the present invention and in the case of not embedding thevector C₀ in the codebook as in the conventional one. In Table 1, theaxis of ordinate is cepstrum distortion, which corresponds to the logspectrum distortion, shown in decibel (dB). The smaller cepstrumdistortion is, the better the quantization performance is. Also, as thespeech intervals for computing the distortion, the mean distortions arefound in the average of all of the intervals (Total), in the intervalother than the silent interval and the stationary interval of the speech(Mode 0), and in the stationary interval of the speech (Mode 1). One inwhich the silent interval exists is Mode 0, and regarding thedistortions therein, that of the proposed codebook is 0.11 dB lower, andit is understood that there is the effect by inserting the silent andzero vectors. Also, regarding the cepstrum distortion in Total, thedistortion in case of using the proposed codebook is lower, and sincethere is no deterioration in the speech stationary interval, theeffectiveness of the codebook according to the present invention isobvious.

[0168] As described above, according to the present invention, in codingwherein the parameter equivalent to the linear predictive coefficient isquantized by the weighted sum of the code vector of the current frameand the code vector outputted in the past, or the vector in which theabove sum and mean vector found in advance are added together, as thevector stored in the vector codebook, the parameter vector correspondingto the silent interval or the stationary noise interval, or a vector inwhich the aforementioned mean vector is subtracted from the parametervector is selected as the code vector, and the code thereof can beoutputted. Therefore, there can be provided the coding and decodingmethods and the devices thereof in which the quality deterioration inthese intervals is scarce.

1. An acoustic parameter coding method, comprising: (a) a step ofcalculating an acoustic parameter equivalent to a linear predictivecoefficient showing a spectrum envelope characteristic of an acousticsignal for every frame of a predetermined length of time; (b) a step ofmultiplying a code vector outputted in at least one frame in the closestpast selected from a vector codebook for storing a plurality of codevectors in correspondence with an index representing said code vectorsand a code vector selected in a current frame respectively with a set ofweighting coefficients selected from a coefficient codebook for storingone or more sets of weighting coefficients in correspondence with anindex representing the weighting coefficients, wherein multipliedresults are added to generate a weighted vector and a vector including acomponent of said weighted vector is found as a candidate of a quantizedacoustic parameter with respect to said acoustic parameter of thecurrent frame; and (c) a step of determining the code vector of thevector codebook and the set of the weighting coefficients of thecoefficient codebook by using a criterion such that a distortion of saidcandidate of the quantized acoustic parameter with respect to thecalculated acoustic parameter becomes a minimum, wherein an indexshowing the determined code vector and the determined set of theweighting coefficients are determined and outputted as a quantized codeof the acoustic parameter; wherein said vector codebook includes avector having a component of an acoustic parameter vector showing asubstantially flat spectrum envelope as one of the stored code vectors.2. In the coding method according to claim 1, said vector codebook isformed of codebooks in plural stages each storing a plurality of vectorsin correspondence with an index representing the vectors, a codebook atone stage of said codebooks in the plural stages stores said vectorincluding the component of the acoustic parameter vector showing thesubstantially flat spectrum envelope as one of the stored vectors,another codebook at another stage of the codebooks in the plurality ofstages stores a zero vector as one of the stored vectors, and said step(b) includes a step of respectively selecting vectors from the codebooksin the plural stages and adding the selected vectors together to therebyoutput an added result as said vector selected in the current frame. 3.In the coding method according to claim 1, said vector codebook isformed of codebooks in plural stages each storing a plurality of vectorsin correspondence with an index representing the vectors, a codebook atone stage of the codebooks in the plural stages stores said vectorincluding the component of the acoustic parameter vector showing thesubstantially flat spectrum as one of the stored vectors, said step (b)further includes a step of respectively selecting vectors from thecodebooks in the plural stages when a code vector other than said vectorincluding the parameter vector is selected from the codebook at said onestage of the codebooks in the plural stages and adding the selectedvectors together to thereby output an added result as the code vectorselected in the current frame, wherein in case said vector including thecomponent of the acoustic parameter vector showing the substantiallyflat spectrum envelope is selected from the codebook at said one stage,said vector including the component of the acoustic parameter vectorshowing the substantially flat spectrum envelope is outputted as saidvector selected in the current frame.
 4. In the coding method accordingto claim 2 or 3, a codebook of at least one of the stages of thecodebooks in the plural stages includes a plurality of split vectorcodebooks for divisionally storing a plurality of split vectors in whichdimensions of code vectors are divided in plural, and an integratingpart for integrating the split vectors outputted from the plurality ofsplit vector codebooks to thereby output the same as an output vector ofthe codebook of the corresponding stage.
 5. In the coding methodaccording to claim 2 or 3, said vector including the component of theacoustic parameter vector showing the substantially flat spectrumenvelope is a vector generated by subtracting a mean vector ofparameters equivalent to the linear predictive coefficient in anentirety of the acoustic signal and found in advance from said parametervector equivalent to the linear predictive coefficient.
 6. In the codingmethod according to claim 1, said vector codebook includes codebooks inplural stages each storing a plurality of code vectors, and scalingcoefficient codebooks respectively provided with respect to therespective codebooks of a second stage and stages after the secondstage, each of said scaling coefficient codebooks storing scalingcoefficients determined in advance in accordance with respective codevectors of a codebook at a first stage, a codebook at one stage of saidcodebooks in the plural stages stores said vector including thecomponent of the acoustic parameter vector showing the substantiallyflat spectrum as one of the stored vectors, each of other codebooks ofthe remaining stages storing a zero vector, wherein said step (b)comprises: a step of reading out scaling coefficients from the scalingcodebooks on and after the second stage in correspondence with a codevector selected at the first stage, and multiplying the code vectorselected at the first stage with each of the selected code vectors, tothereby output multiplied results as vectors of the respective stages;and a step of adding the outputted vectors of the respective stages tothe vector at the first stage, to thereby output an added result as acode vector from the vector codebook.
 7. In the coding method accordingto any one of claims 2, 3 and 5, said steps (b) and (c) collectivelyinclude firstly a step of searching a predetermined number of codevectors such that a distortion due to the code vector selected from thecodebook of said one stage is a minimum, and subsequently a step offinding said distortions for all of combinations between saidpredetermined number of the code vectors and code vectors each beingselected one by one from codebooks of the remaining stages, to therebydetermine a code vector of a combination in which the distortion becomesthe minimum.
 8. In the coding method according to claim 6, a codebook atleast one stage on and after the second stage among said codebooks inthe plural stages is formed of a plurality of split vector codebooksdivisionally storing a plurality of split vectors in which dimensions ofthe code vectors are divided in plural, said scaling coefficientcodebook corresponding to the codebook of said at least one stageincludes a plurality of scaling coefficient codebooks for the splitvectors provided with respect to the plurality of split vectorcodebooks, and scaling coefficients for split vectors in which each ofcode vectors of the respective scaling coefficient codebooks for thesplit vectors is found in advance with respect to each of the codevectors of the codebook at the first stage, wherein said step (b)comprises: a step of reading out a scaling coefficient for a splitvector in correspondence with the index of the vector selected at thecodebook of the first stage and respectively multiplying the same withsplit vectors respectively selected from the plurality of split vectorcodebooks of said at least one stage; and a step of integrating splitvectors obtained by said multiplying to thereby output integratedresults as output vectors of the codebooks at the respective stages. 9.In the coding method according to claim 1, said vector codebook isformed of a plurality of split vector codebooks in which dimensions ofthe code vectors are divided in plural, and an integrating part forintegrating split vectors outputted from the split vector codebooks tothereby output a result as one code vector, said vector including thecomponent of the acoustic parameter vector showing the substantiallyflat spectrum envelope is divisionally stored in each of the pluralityof split vector codebooks as a split vector.
 10. In the coding methodaccording to claim 1, said vector including the component of theacoustic parameter vector showing the substantially flat spectrumenvelope is a vector generated by subtracting said mean vector from saidacoustic parameter vector showing the linear predictive coefficient, andsaid step (b) includes a step of adding said weighted vector to a meanvector of parameters equivalent to the linear predictive coefficient inan entirety of the acoustic signal found in advance, to thereby generatethe vector including the component of the weighted vector.
 11. In thecoding method according to claim 1, the parameter equivalent to thelinear predictive coefficient constitutes an LSP parameter.
 12. Anacoustic parameter decoding method, comprising: (a) a step of outputtinga code vector corresponding to an index expressed by a code inputted forevery frame and a set of weighting coefficients from a vector codebookand a coefficient codebook, said vector codebook storing a plurality ofcode vectors of an acoustic parameter equivalent to a linear predictivecoefficient showing a spectrum envelope characteristic of an acousticsignal in correspondence with an index representing the code vectors,said coefficient codebook storing one or more sets of weightingcoefficients in correspondence with an index representing said sets; and(b) a step of multiplying said code vector outputted from said vectorcodebook in at least one frame of the closest past and a code vectoroutputted from the vector codebook in a current frame respectively withsaid outputted set of the weighting coefficients, and adding multipliedresults together to thereby generate a weighted vector, wherein a vectorincluding a component of said weighted vector is outputted as a decodedquantized vector of the current frame; wherein said vector codebookincludes a vector having a component of an acoustic parameter vectorshowing a substantially flat spectrum envelope as one of the codevectors stored therein.
 13. In the decoding method according to claim12, said vector codebook is formed of codebooks in plural stages eachstoring a plurality of vectors in correspondence with an indexrepresenting the vectors, a codebook at one stage of the codebooks inplural stages stores said vector including the component of the acousticparameter vector showing the substantially flat spectrum envelope,codebooks of the other stages storing zero vectors as one of thevectors, and said step (b) includes a step of respectively outputtingvectors specified by the index expressed by the inputted code from thecodebooks in the plural stages, in which the outputted vectors are addedand an added result is outputted as a code vector in the current frame.14. In the decoding method according to claim 12, said vector codebookis formed of codebooks in plural stages each storing a plurality ofvectors in correspondence with an index representing the vectors, acodebook at one stage of the codebooks in plural stages stores saidvector including the component of the acoustic parameter vector showingthe substantially flat spectrum envelope as one of the vectors, saidstep (b) includes a step of respectively selecting vectors from thecodebooks in the plural stages when a code vector other than said vectorincluding the component of the acoustic parameter vector showing thesubstantially flat spectrum envelope is selected from the codebook atsaid one stage of the codebooks in the plural stages and adding theselected vectors together to thereby output an added result as the codevector selected in the current frame, wherein in case said vectorincluding the component of the acoustic parameter vector showing thesubstantially flat spectrum envelope is selected from the codebook atsaid one stage, said vector including the component of the acousticparameter vector showing the substantially flat spectrum envelope isoutputted as said vector of the current frame.
 15. In the decodingmethod according to claim 13 or 14, a codebook of at least one of thestages of the codebooks in the plural stages includes a plurality ofsplit vector codebooks for divisionally storing a plurality of splitvectors in which dimensions of code vectors are divided in plural, andan integrating part for integrating the split vectors outputted from theplurality of split vector codebooks to thereby output the same as anoutput vector of the codebook of the corresponding stage.
 16. In thedecoding method according to claim 13 or 14, said vector including thecomponent of the parameter vector equivalent to the linear predictivecoefficient is a vector generated by subtracting a mean vector ofparameters equivalent to the linear predictive coefficient in anentirety of the acoustic signal and found in advance from said parametervector equivalent to the linear predictive coefficient.
 17. In thedecoding method according to claim 12, said vector codebook includescodebooks in plural stages each storing a plurality of code vectors, andscaling coefficient codebooks respectively provided with respect to therespective codebooks of a second stage and stages after the secondstage, each of said scaling coefficient codebooks stores scalingcoefficients determined in advance in correspondence with code vectorsof a codebook at a first stage, a codebook at one stage of saidcodebooks in the plural stages storing said vector including thecomponent of the acoustic parameter vector showing the substantiallyflat spectrum as one of the stored vectors, each of other codebooks ofthe remaining stages storing a zero vector, wherein said step (b)comprises: a step of reading out scaling coefficients from the scalingcodebooks on and after the second stage in correspondence with a codevector selected at the first stage, and multiplying the code vectorselected at the first stage with each of the selected code vectors, tothereby output multiplied results as vectors of the respective stages;and a step of adding the outputted vectors of the respective stages tothe vector at the first stage, to thereby output an added result as acode vector from the vector codebook.
 18. In the decoding methodaccording to claim 17, a codebook at at least one stage on and after thesecond stage among said codebooks in the plural stages is formed of aplurality of split vector codebooks divisionally storing a plurality ofsplit vectors in which dimensions of the code vectors are divided inplural, said scaling coefficient codebook corresponding to the codebookof said at least one stage includes a plurality of scaling coefficientcodebooks for the split vectors provided with respect to the pluralityof split vector codebooks, said scaling coefficient codebook for splitvectors stores a plurality of scaling coefficients for split vectors incorrespondence with the respective code vectors of the codebook of thefirst stage, wherein said step (b) comprises: a step of reading out ascaling coefficient for a split vector in correspondence with the indexof the vector selected at the codebook of the first stage andrespectively multiplying the same with split vectors respectivelyselected from the plurality of split vector codebooks of said at leastone stage, and a step of integrating split vectors obtained by saidmultiplying to thereby output integrated results as output vectors ofthe codebooks at the respective stages.
 19. In the decoding methodaccording to claim 12, said vector codebook is formed of a plurality ofsplit vector codebooks in which dimensions of the code vectors aredivided in plural, and an integrating part for integrating split vectorsoutputted from the split vector codebooks to thereby output a result asone code vector, said vector including the component of the acousticparameter vector showing the substantially flat spectrum envelope isdivided into split vectors to be divisionally stored in each of theplurality of split vector codebooks as a split vector.
 20. In thedecoding method according to claim 12, said vector including thecomponent of the acoustic parameter vector showing the substantiallyflat spectrum envelope is a vector generated in advance by subtractingsaid mean vector from said acoustic parameter vector showing the linearpredictive coefficient, and said step (b) includes a step of adding saidweighted vector and a mean vector of parameters equivalent to the linearpredictive coefficient in an entirety of the acoustic signal found inadvance, to thereby generate the vector including the component of theweighted vector.
 21. In the decoding method according to claim 12, theparameter equivalent to the linear predictive coefficient constitutes anLSP parameter.
 22. An acoustic parameter coding device, comprising:parameter calculating means for analyzing an input acoustic signal forevery frame and calculating an acoustic parameter equivalent to a linearpredictive coefficient showing a spectrum envelope characteristic of theacoustic signal; a vector codebook for storing a plurality of codevectors in correspondence with an index representing the vectors; acoefficient codebook for storing one or more sets of weightingcoefficients in correspondence with an index representing thecoefficients; quantized parameter generating means for multiplying acode vector with respect to a current frame outputted from the vectorcodebook and a code vector outputted in at least one frame of theclosest past respectively with the set of the weighting coefficientsselected from the coefficient codebook, said quantized parametergenerating means adding results together to thereby generate a weightedvector, said quantized parameter generating means outputting a vectorincluding a component of the generated weighted vector as a candidate ofa quantized acoustic parameter with respect to the acoustic parameter inthe current frame; a distortion computing part for computing adistortion of the quantized acoustic parameter with respect to theacoustic parameter calculated at the parameter calculating means; and acodebook search controlling part for determining the code vector of thevector codebook and the set of the weighting coefficients of thecoefficient codebook by using a criterion such that the distortionbecomes small, said codebook search controlling part outputting indexesrespectively representing the determined code vector and the set of theweighting coefficients as codes of the acoustic parameter; wherein saidvector codebook includes a vector having a component of an acousticparameter vector showing a substantially flat spectrum envelope.
 23. Inthe coding device according to claim 22, said vector codebook includescodebooks in plural stages each storing a plurality of vectors incorrespondence with an index representing the vectors, and an adder foradding the vectors outputted from the codebooks in the plural stages tothereby output the code vector, a codebook at one stage of the codebooksin the plural stages stores said vector including the component of theacoustic parameter vector showing the substantially flat spectrumenvelope, and other codebooks at the other stages store a zero vector asone of the code vectors.
 24. In the coding device according to claim 23,said codebook of at least one stage among the codebooks in the pluralstages is formed of a plurality of split vector codebooks fordivisionally storing a plurality of split vectors in which dimensions ofthe code vectors are divided in plural in correspondence with the indexrepresenting the split vectors, and an integrating part for integratingthe split vectors outputted from the plurality of the split vectorcodebooks to thereby output a result as an output vector of the codebookof the stage.
 25. In the coding device according to claim 22, saidvector codebook comprises: codebooks in plural stages each storing aplurality of code vectors in correspondence with an index representingthe vectors; scaling coefficient codebooks provided at respectivecodebooks on and after the second stage and storing scaling coefficientsdetermined in advance by corresponding to the respective code vectors ofthe codebook of the first stage in correspondence with an indexrepresenting the coefficients; multiplying means reading out acorresponding scaling coefficient from the scaling codebook with respectto the codebooks on and after the second stage, said multiplying meansmultiplying the code vector selected at the first stage with the codevector respectively selected from the codebooks on and after the secondstage, to thereby output multiplied results as vectors of the respectivestages; and an adder for adding vectors of the respective stagesoutputted from the multiplying means to the vector of the first stage,said adder outputting an added result as the code vector from the vectorcodebook; wherein a codebook of one stage of the codebooks in the pluralstages stores the vector including the component of the acousticparameter vector showing said substantially flat spectrum envelope, andcodebooks at the remaining stages store a zero vector.
 26. In the codingdevice according to claim 25, a codebook of at least one stage on andafter the second stage among said codebooks in the plural stages isformed of a plurality of split vector codebooks for divisionally storinga plurality of split vectors in which dimensions of the code vectors aredivided in plural, wherein said scaling coefficient codebookcorresponding to the codebook of said at least one stage comprises: aplurality of scaling coefficient codebooks for split vectors storing aplurality of scaling coefficients for split vectors, which are providedin plural to correspond to the plurality of the split vector codebooks,respectively in correspondence with the code vectors of the first stage;multiplying means for multiplying split vectors respectively outputtedfrom the plurality of split vector codebooks of said at least one stagerespectively with the scaling coefficient for split vectorscorresponding to the index of the vector selected at the codebook of thefirst stage by reading out said scaling coefficient from the respectivescaling coefficient codebooks for split vectors; and an integrating partfor integrating multiplied results to thereby output a result as anoutput vector of the codebook of the corresponding stage.
 27. In thecoding device according to claim 22, said vector codebook is formed of aplurality of split vector codebooks for divisionally storing a pluralityof split vectors in which dimensions of the code vectors are divided inplural, and an integrating part for integrating split vectors outputtedfrom the split vector codebooks and outputting a result as one codevector; and said vector including the component of the acousticparameter vector showing the substantially flat spectrum envelope isdivided into split vectors to be stored one by one as the split vectorsin the plurality of the split vector codebooks.
 28. An acousticparameter decoding device, comprising: a vector codebook for storing aplurality of code vectors of an acoustic parameter equivalent to alinear predictive coefficient showing a spectrum envelope characteristicof an acoustic signal in correspondence with an index representing thecode vectors, a coefficient codebook for storing one or more sets ofweighting coefficients in correspondence with an index representing theweighting coefficients, and quantized parameter generating means foroutputting one code vector from the vector codebook in correspondencewith an index showing a code inputted for every frame, to thereby outputa set of weighting coefficients from said coefficient codebook, saidquantized parameter generating means multiplying the code vectoroutputted in a current frame and a code vector outputted in at least oneframe of the closest past respectively with the set of the weightingcoefficients outputted in the current frame, said quantized parametergenerating means adding multiplied results together to thereby generatea weighted vector, said quantized parameter generating means outputtinga vector including a component of the generated weighted vector as adecoded quantized acoustic parameter of the current frame; wherein saidvector codebook stores a vector including a component of an acousticparameter showing a substantially flat spectrum envelope as one of thecode vectors.
 29. In the decoding device according to claim 28, saidvector codebook is formed of codebooks in plural stages each storing aplurality of vectors in correspondence with an index representing theplurality of vectors, and an adder for adding the vectors outputted fromthe codebooks in the plural stages to thereby output a code vector, anda codebook at one stage of the codebook in the plural stages stores thevector including the component of the acoustic parameter vector showingthe substantially flat spectrum envelope as one of the vectors, andcodebooks at other stages store a zero vector as one of the codevectors.
 30. In the decoding device according to claim 29, a codebook ofat least one stage among said codebooks in the plural stages includes aplurality of split vector codebooks for divisionally storing a pluralityof split vectors in which dimensions of the code vectors are divided inplural, and an integrating part for integrating split vectors outputtedfrom said plurality of split vector codebooks to thereby output a resultas an output vector of a codebook of a corresponding stage.
 31. In thedecoding device according to claim 28, said vector codebook comprises:codebooks in plural stages each storing a plurality of code vectors incorrespondence with an index representing the code vectors; scalingcodebooks each being provided with respect to respective codebooks onand after a second stage and storing scaling coefficients determined inadvance corresponding to code vectors of the codebook of a first stagein correspondence with an index representing the scaling coefficients;multiplying means for reading out a corresponding scaling coefficientfrom the scaling codebook with respect to the codebook on and after thesecond stage in correspondence to the code vector selected at the firststage, said multiplying means multiplying the code vectors respectivelyselected from the codebooks on and after the second stage with the readout scaling coefficient to thereby output multiplied results as vectorsof the respective stages; and an adder for adding the output vectors ofthe respective stages outputted from the multiplying means to the vectorat the first stage, to thereby output an added result as a code vectorfrom the vector codebook; wherein a codebook of one stage among thecodebooks in the plural stages stores said vector including thecomponent of the acoustic parameter vector showing the substantiallyflat spectrum envelope, and codebooks of the remaining stages store azero vector.
 32. In the decoding device according to claim 31, acodebook at least one stage on and after the second stage among thecodebooks in the plural stages is formed of a plurality of splitcodebooks for divisionally storing a plurality of split vectors in whichdimensions of code vectors are divided in plural, and said scalingcoefficient codebook corresponding to the codebook of said at least onestage comprises: a plurality of scaling coefficient codebooks for splitvectors storing scaling coefficients for a plurality of split vectorsprovided in plural corresponding to said plurality of split vectorcodebooks to respectively correspond to code vectors in the first stage;multiplying means for reading out scaling coefficients for split vectorscorresponding to an index of the vector selected at the codebook of thefirst stage from the respective scaling coefficient codebooks for thesplit vectors, said multiplying means respectively multiplying splitvectors respectively outputted from said plurality of split vectorcodebooks of said at least one stage with the scaling coefficients forsplit vectors; and an integrating part for integrating multipliedresults and outputting a result as an output vector of a codebook of acorresponding stage.
 33. In the decoding device according to claim 28,the vector codebook comprises a plurality of split vector codebooks fordivisionally storing a plurality of split vectors in which dimensions ofcode vectors are divided in plural, and an integrating part forintegrating split vectors outputted from the split vector codebooks tothereby output a result as one code vector, wherein: the vectorincluding the component of said acoustic parameter vector showing saidsubstantially flat spectrum envelope is divided into split vectors eachbeing divisionally stored in each of said plurality of vector codebooks.34. An acoustic signal coding device for encoding an input acousticsignal, comprising: means for encoding a spectrum characteristic of aninput acoustic signal by using the acoustic parameter coding methodaccording to claim 1; an adaptive codebook for holding adaptive codevectors showing periodic components of said input acoustic signaltherein; a fixed codebook for storing a plurality of fixed vectorstherein; filtering means for inputting as an excitation signal a soundsource vector generated based on the adaptive code vector from theadaptive codebook and the fixed vector from the fixed codebook, saidfiltering means synthesizing a synthesized acoustic signal by using afilter coefficient based on said quantized acoustic parameter; and meansfor determining an adaptive code vector and a fixed code vectorrespectively selected from the fixed codebook and the adaptive codebooksuch that a distortion of the synthesized acoustic signal with respectto said input acoustic signal becomes small, said means outputting anadaptive code and a fixed code respectively corresponding to thedetermined adaptive code vector and the fixed vector.
 35. An acousticsignal decoding device for decoding an input code and outputting anacoustic signal, comprising: means for decoding an acoustic parameterequivalent to a linear predictive coefficient showing a spectrumenvelope characteristic from an inputted code by using the acousticparameter decoding method according to claim 12; a fixed codebook forstoring a plurality of fixed vectors therein; an adaptive codebook forholding adaptive code vectors showing periodic components of asynthesized acoustic signal therein; means for taking out acorresponding fixed vector from the fixed codebook and taking out acorresponding adaptive code vector from the adaptive codebook by aninputted adaptive code and an inputted fixed code, the meanssynthesizing the vectors and generating an excitation vector; andfiltering means for setting a filter coefficient based on the acousticparameter and reproducing an acoustic signal by the excitation vector.36. An acoustic signal coding method for encoding an input acousticsignal, comprising: (A) a step of encoding a spectrum characteristic ofan input acoustic signal by using the acoustic parameter coding methodaccording to claim 1; (B) a step of using as an excitation signal asound source vector generated based on an adaptive code vector from anadaptive codebook for holding adaptive code vectors showing periodiccomponents of an input acoustic signal therein and a fixed vector from afixed codebook for storing a plurality of fixed vectors therein, andcarrying out a synthesis filter process by a filter coefficient based onsaid quantized acoustic parameter to thereby generate a synthesizedacoustic signal; and (C) a step of determining an adaptive code vectorand a fixed vector selected from the fixed codebook and the adaptivecodebook such that a distortion of the synthesized acoustic signal withrespect to the input acoustic signal becomes small, and outputting anadaptive code and a fixed code respectively corresponding to thedetermined adaptive code vector and the fixed vector.
 37. An acousticsignal decoding method for decoding input codes and outputting anacoustic signal, comprising: (A) a step of decoding an acousticparameter equivalent to a linear predictive coefficient showing aspectrum envelope characteristic from inputted codes by using theacoustic parameter decoding method according to claim 12; (B) a step oftaking out a corresponding adaptive code vector from an adaptivecodebook for holding therein adaptive code vectors showing periodiccomponents of an input acoustic signal by an adaptive code and a fixedcode among the inputted codes, taking out a corresponding fixed vectorfrom a fixed codebook for storing a plurality of fixed vectors therein,and synthesizing the adaptive code vector and the fixed vector tothereby generate an excitation vector; and (C) a step of carrying out asynthesis filter process of the excitation vector by using a filtercoefficient based on the acoustic parameter, and reproducing asynthesized acoustic signal.
 38. A program for conducting the acousticparameter coding method according to any one of claims 1 to 11 by acomputer.
 39. A program for conducting the acoustic parameter decodingmethod according to any one of claims 12 to 21 by a computer.
 40. Anacoustic signal transmission device, comprising: an acoustic inputdevice for converting an acoustic signal into an electric signal; an A/Dconverter for converting the signal outputted from the acoustic inputdevice into a digital signal; the acoustic signal decoding deviceaccording to claim 34 for encoding the digital signal outputted from theA/D converter; an RF modulator for conducting a modulation process andthe like with respect to encoded information outputted from the acousticsignal coding device; and a transmitting antenna for converting thesignal outputted from the RF modulator into a radio wave andtransmitting the same.
 41. An acoustic signal receiving device,comprising: a receiving antenna for receiving a reception radio wave; anRF demodulator for conducting a demodulation process of the signalreceived by the receiving antenna; the acoustic signal decoding deviceaccording to claim 35 for conducting a decoding process of informationobtained by the RF demodulator; a D/A converter for converting a digitalacoustic signal decoded by the acoustic signal decoding device; and anacoustic signal outputting device for converting an electric signaloutputted from the D/A converter into an acoustic signal.